ATP-sensitive potassium (KATP) channels are participants in the response of the heart and vascular system to change of metabolic state, including ischemia. This project seeks to understand the regulation and role of ATP-sensitive potassium channels in the intact heart. The work conducted during the previous period of award provided significant new discoveries regarding the molecular basis of KATP channel function. We have made use of these discoveries to develop novel transgenes that allow us to express over- and under-active mutant KATP channels in cardiac sarcolemmal membranes. We have generated transgenic mice in which the sarcolemmal KATP channel properties are significantly changed, and have begun to explore the consequences for cardiac function. In order to extend preliminary data, we now propose three experimental series, addressing the following questions: (1) What are the cellular consequences of altered ATP-sensitivity of KATP channels on cardiac myocyte function? (2) How do SUR2A and cellular environment confer the cardiac KATP channel phenotype? 3) What is the role of the sarcolemmal KATP channel in normal and patho-physiology of the heart? Work on this project to date, has contributed substantially to current understanding of the role and molecular basis of KATP channels. The results of the proposed experiments will bring insight to the role of these channels in the heart in vivo. The work will provide information that will ultimately underlie the development of rational therapies for the treatment of cardiac ischemia and arrhythmias.